A. Nosocomial Infections
A nosocomial infection (NI) is defined as a disease acquired by a patient at a health care facility (i.e. not the patient's original disorder). Many NI are caused by microorganisms that can naturally colonize the external surfaces of the body (e.g. skin, moist mucosal surfaces or GI tract), however, under certain conditions these "opportunists" can cause disease. For example, NI are often associated with invasive medical procedures, such as surgery and bronchoscopy, and with penetrating devices, such as catheters. Furthermore, intensive care patients are particularly at risk of NI, especially in surgical, pediatric/neonatal, burns and trauma units (Martin, M.A. New Horizons 1:162-171, (1993)). The predominant causes of NI are gram positive bacteria (&gt;40%), especially Staphylococcus aureus and Staphylococcus epidermidis, and gram negative bacteria (&gt;40%), especially Escherichia coli, with the remaining NI being caused mainly by yeast and fungi (Vermaat et al. American Journal of Infection Control 21:183-188, (1993)). Gram positive bacteria, such as Staph. aureus, are of particular concern due to their hardiness (ability to survive under non-physiologic conditions) and their inherent resistance to many antibiotics. Each year, NI affect an approximately 2 million patients, cause more than 60,000 deaths and incur an estimated $4.5 billion in added costs (Morbidity and Mortality Weekly Reports 41:783-787, (1992); Pittet, D. & Wenzel, R. P. Archives of Internal Medicine 155:1177-1184, (1995)). These figures have been increasing progressively over the last 10 years.
A component of NI that is an increasing problem is the incidence of drug-resistant microorganisms. This problem is highlighted in a recent monologue by Stuart B. Levy, M.D. (Levy, S. B., The Antibiotic Paradox. How Miracle Drugs are Destroying the Miracle., Plenum Press, New York (1992)), which describes a number of case studies involving outbreaks of multi-drug resistant (MDR) strains of bacteria. One example of this is the "golden staph" or methicillin-resistant Staphylococcus aureus (MRSA). The incidence of MRSA varies between health care facilities and countries, however, it can be greater than 50% of all Staph. aureus isolates, and appears to be increasing, especially in Japan (Lotsu et al. Jour. Hosp. Infection, 27:275-283, (1995)). Disease caused by MRSA can be effectively treated with vancomycin, however, there is concern that inappropriate use of this antibiotic may lead to the emergence of vancomycin-resistant MRSA. Disease caused by this organism will be extremely difficult to treat, tantamount to a death sentence.
The incidence of NI, including MRSA, can be reduced by at least 30% by implementing suitable infection control measures, however, in the US, only 6%-9% of NI are actually being prevented (Hospital Infections Program, Centers for Disease Control and Prevention). Of particular concern is the fact that a common reservoir for MRSA is the nasal passages of health care workers, with hand contamination often being the route of transfer (Guidelines for management of patients with methicillin-resistant Staphylococcus aureus in acute care hospitals and long-term care facilities. Connecticut Medicine 57:611-617 (1993); Wenzel, R. P. Journal of Chemotherapy 6 suppl. 4:33-40, (1994)). Consequently, a major component of successful infection control programs is an emphasis on hand washing and effective use of sterilizing procedures, disinfectants and antiseptics (CDC Guidelines for Handwashing and Hospital Environmental Control).
Gram-negative microorganisms, as exemplified by Salmonella, Pseudomonas, and virulent strains of E. coli, are also important bacteria both clinically and also to the food industry. Salmonella is a major cause of food poisening--caused by the ingestion of meat (or items in contact with the meat) of diseased animals. Pseudomonas is widely distributed in water and air, on the skin and in the upper respiratory tract, and can be isolated from feces. It is clinically associated with other pyrogenic organisms in abdonimal acscesses, and can cause cystitis, otitis media, mastoiditis, enteritis in children and even septicemia.
As with gram positive microorganisms, such infections can be extremely difficult to treat. Prevention of such infections, especially clinically and in the food industry, is grounded on the effective use of sterilizing procedures, disinfectants and antiseptics. The effective use of reagents that could be used as disinfectants, or more importantly antiseptics, that could efficiently eliminate pathogenic microorganisms would help to alleviate the burden of medical costs attributable to such infections.
B. Disinfectants and Antiseptics
Germicidal activities are generally discussed in terms of sterilization, disinfectant properties and antiseptic qualities. Sterilization involves the use of chemical or physical means to totally eliminate microorganisms, viruses, fungi, spores, yeast and other saprophytic and infectious agents, independent of type or classification (e.g., autoclaving or irradiation).
Disinfectants are, by definition, germicidal agents used on inanimate objects. Disinfectants are typically chemical agents that are generally less broad in terms of their spectrum of activity, relative to sterilizing procedures. As a result, not all forms of a given category of organism are killed, but pathogenic forms are preferentially eliminated by design.
Antiseptics are, by definition, germicidal agents designed for use on living or biological tissue, primarily skin and hair. Antiseptics are typically milder chemical agents than disinfectants and, as a result, are generally less efficacious at eliminating infectious agents. For example, disinfectants usually incorporate organic reagents that would be unacceptable in antiseptic formulations due to toxicity, carcinogenic or mutagenic activity. Since routes of infection are typically through a breach in tissue, or via a natural opening, antiseptic formulations provide perhaps the most important line of defense.
Unfortunately, the dichotomy between toxicity and efficacy precludes many disinfectants from being used as antiseptics. Additionally, many microbial pathogens are resistant to commonly used disinfectants and antiseptics. There is a need for bactericidal compositions, especially disinfectant and antiseptic compositions, that are efficacious, and that are economical to make and use.
C. Detergents as Disinfectants and Antiseptics
In general, nonionic detergents have been reported to have minimal, if any, bactericidal activity, whereas ionic detergents, such as the quaternary amines, have been reported to have bactericidal activity (Cella, J. A. et al., J Am. Chem. Soc. 74:2061-2062 (1952)). Cella also reported that, in general, quaternary amine detergents that have longer alkyl chains also have greater bactericidal activity than their shorter chain counterparts.
However, ionic detergents are generally untenable as components in aqueous antiseptic and disinfectant formulations due to a lack of solubility in the presence of ions. If provided in the precipitated form, the reagent is less available and less efficacious. Nonionic detergents are, for the most part, unaffected by the presence of ions so, at a first glance, would appear to be suitable for antiseptic and disinfectant preparations. However, such detergents are not ideal for the purposes of decontamination, due to their relatively poor bactericidal activity.
A decrease in solubility in the presence of ions is called "salting-out." When ionic detergents are placed in the presence of ions (e.g., NaCl), there is a "Krafft point elevation" (e.g. the temperature required to maintain the detergent in solution is increased). In other words, the heat of mixing required to maintain the detergent molecules in solution is increased; below the Krafft point, the detergent precipitates (or "salts") out of solution.
As an example of salting-out, the temperature required to maintain C.sub.12 -sulfonate in solution in pure water is 31.5.degree. (Tartar, H. V et al., Jour. Am. Chem. Soc. 61:539-544 (1939)), but 34.degree. C. in 8 mM salt (Tartar, H. V. et al., Jour. Phys. Chem. 43:1173-1179 (1939)). Thus, the Krafft point elevation, or "salting-out effect," is 3.5.degree. C. under these conditions. The salting-out behavior of C.sub.14 -sulfonate occurs at 39.5.degree. C. and 43.degree. C. in water and saline, respectively (Tartar, H. V et al., Jour. Am. Chem. Soc. 61:539-544 (1939), Tartar, H. V. et al., Jour. Phys. Chem. 43:1173-1179 (1939)). The Krafft temperature of C.sub.18 -sulfonate in pure water begins at 57.degree. C. (Tartar, H. V et al., Jour. Am. Chem. Soc. 61:539-544 (1939)).
Betaines are zwitterionic detergents and are commonly found in commercial preparations of soaps, shampoos, laundry detergents, cosmetics and other toiletries. In addition to their use as surface active agents, it has been reported that certain of the n-alkyl betaines have bactericidal activity. Betaines have been used as antimicrobials in commercial formulations of antioxidants (Nemcova, J., et al. CS 202494 B), cleansers (Gomi, T. JP 8895298 2; JP 6395198) and detrifice preparations (Oshino K., et al., JP 92134025 A2; JP 04134025).
Voss et al. J. Gen. Microbiol. 48:391-400 (1967) reported on the bactericidal activity of sulfopropylbetaines, and Tsubone et al. J. Phar. Sci. 80:441-444 (1991) studied the action of phosphatobetaines. Tsubone reported that both C.sub.16 -phosphatoethylbetaine and C.sub.16 -phosphatobutylbetaine have greater bactericidal activity than C.sub.16 -phosphatopropylbetaine. C.sub.16 -phosphatoethylbetaine had the highest degree of bactericidal activity of those Tsubone tested. Unfortunately, solubility can be a problem with the longer chains on these betaines.
Since the n-alkyl betaines have been used in both topical emollients and antimicrobial formulations, they appear to be attractive candidates for inclusion into disinfectant and antiseptic preparations. However, there are limitations, such as the salting out characteristic discussed above, and others as discussed further herein, that have prevented the widespread effective commercial use of n-alkyl betaines in antiseptic and disinfectant concoctions.
D. Betaine Chemistry
The most common n-alkyl betaines utilize natural oils as the alkyl chain (e.g., coconut oil), and the charges are usually separated by a methylene bridge. Coco-carboxymethylbetaine is probably the most common commercially available betaine, and is a primary component of many shampoo formulations.
The betaine detergents, as a group, are extremely heterogeneous with respect to structure and composition. For example, there are n-alkyl betaines that incorporate phosphates (e.g., phosphatobetaines), phosphonates (e.g., phosphonobetaines), and phosphinates (e.g., phosphinobetaines), sulfates (e.g., sulfatobetaines), sulfonates (e.g., sulfobetaines), and oxide radicals (e.g., amine oxides) as the anion. The structure of the "bridge" (e.g., "R.sub.4 " (see Table 1)) separating the charges can include, in addition to methylene, ethylene, propylene, butylene, and longer hydrocarbon-like chains, aromatic or hydroxyl groups, or even a simple covalent bond, as in the case of amine oxides. Further, it is not uncommon to have aminopropyl or carbonyl functions "linking" (e.g., ".alpha." (see Table 1)) the alkyl chain to the ammonium.
The physical properties of n-alkyl betaines are entirely dependent on structure. For example, changing the anion from a sulfate, to a sulfonate, to a carboxylate, to a phosphate, causes a change in character from that of a nonionic detergent to that of an ionic detergent. The sulfato-betaine is extremely nonionic in nature, whereas the sulfonate has both ionic and nonionic characteristics (Nilsson, P. et al., J. Phys. Chem. 88:6357-6362 (1984)). Alternatively, the carboxy- and phosphato-betaines are completely ionic in nature with the phosphatobetaine being the extreme ionic example (Tsubone, K. et al., J. Am. Oil. Chem. Soc. 67:394-399 (1990)). Betaines can also be swayed toward a nonionic or ionic character depending on other structural moieties on the molecule (e.g., the bridge (R.sub.4 ; see Table 1) or the linkage (.alpha.)).
One unique aspect of betaine behavior that separates this class of detergents from both ionic and nonionic detergents is the fact some betaines can be "salted-in," as opposed to the ionic detergents, which are "salted-out." If a compound is salted-in, the detergent becomes more soluble (i.e., the Krafft temperature is reduced) in the presence of salt. Betaines that have been commonly used in commercial preparations have been of the salting out type; that is, they would not be soluble in the ionic conditions commonly found in antiseptic and disinfectant compositions.
Betaines with bridge lengths less than 4.about.5 .ANG. typically salt-out in the presence of salt (e.g., similar to ionic detergents). Betaines using a methylene bridge (i.e., R.sub.4 is --CH.sub.2 --) have a charge separation of approximately 3.1 .ANG.(Tsujii, K. et al., Yakagaku 30:495-499 (1981)). The carboxymethylbetaines of Michaels (U.S. Pat. No. 4,062,976, U.S. Pat. No. 4,075,350, U.S. Pat. No.4,107,328, U.S. Pat. No. 4,145,436, U.S. Pat. No. 4,183,952, U.S. Pat. No. 4,839,158, U.S. Pat. No. 5,244,652 and U.S. Pat. No. 5,389,676) have a bridge length of less than 4.about.5 .ANG. and thus would behave in a manner similar to anionic detergents and be of the salting-out type.
Salting-in behavior is extremely dependent on bridge length and structure. N-dodceyl amino-propionic acid possesses the carboxylate anion with an ethylene bridge (i.e., R.sub.4 in Table 1 is --C.sub.2 H.sub.4 --). Tsujii, K. et al., Yakagaku 30:495-499 (1981) report that the distance separating the charges in N-dodecylamino-propionic acid is 4.5 .ANG., and that this detergent is of the salting-in type.
Thus, no one class of betaines has been reported to have the desired combination of bactericidal activity, aqueous solubility, and ease of manufacture that is necessary to facilitate the wide-spread economical commercial use of n-alkyl betaines in antiseptic and disinfectant concoctions.